This invention relates to an information processing system of a battery driven type, for example, a portable terminal equipment or a portable personal computer.
In a prior art information processing system of this kind, a single CPU only was used to carry out all the kinds of processings including application program execution, data communication control, keyboard input monitoring, timer output counting, and power supply monitoring and control. Further, the prior art information processing system was constructed so that, when the power supply was turned on and maintained in the on state, the main CPU was continuously placed in its operation mode consuming a large amount of power, and the power supply voltage had to be supplied also to input/output units not in use.
As described above, in the prior art information processing system in which the CPU carried out all the kinds of processings, those kinds of processing, such as, key input monitoring, timer output counting and power supply monitoring, that are required to be executed at time intervals of a short period, had also to be executed during execution of a program such as an application program. For example, these kinds of processings had to be executed at time intervals of 10 msec while interrupting the execution of the application program by the main CPU.
Further, because the main CPU consuming a large amount of power had to be continuously placed in its operation mode even when the system was waiting arrival of a key input, a large amount of power was wastefully consumed especially in the case of the portable information processing system designed primarily for the purpose of data input processing.
Further, whenever the power supply for the information processing system proper was turned on, the power supply voltage was supplied to all the input/output units in the system. Thus, the power was wastefully supplied also to the input/output units not in use. For example, even when the system was working for data communication for a long time through a modem, the power supply voltage had to be supplied to all the other input/output units including a display unit, a floppy disk drive (referred to hereinafter as an FDD), and an extension slot connected to an external circuit.